leaders are forst to become the instructional leaders given the pressure from NCLB, the leader as the transformer and the culture builder only are not hip anymore. its all about results now

This is a thought provoking question. However it is imperative to note that "leadership style" need not be the issue, how leaders perform the task of leading is the most important of them all. This means that we ought to be seeking to understand the leadership practices that are most popular among school leaders.

No leadership is better than the other but some are exercised more than others given the shift in demographics or needs of the community.

Yes, I agree that no style can be chosen for the top. All can and should be used at different times and situations.

But which do you think should be used mostly?

Practical leadership should be used mostly so students, communities and school practice can trasform

A good question but perhaps one that assumes all school leaders assume a leadership style. Many probably consider themselves a head teacher but don't talk in terms of leadership. But of course they should since they are in a leadership position. I would recommend the work of Professor John Adair and his concept of Action-centered leadership. Here, leaders have to focus on three elements simultaneously: the task, the team and the individual. They must ensure that the task (for example curriculum development) is done; they must also ensure that the team works effectively; but they must also what out for and help individuals. Here coaching can often be effective.

While the teacher is touted as the biggest influence on student achievement (outside the home) the role of leadership cannot be dismissed. Leaders must use a variety of styles (if that is the right concept?) to achieve their goals. Throughout the day to day grind a leader may need to be charismatic, innovative, authoritative, laissez-faire, servant, transformative, (among many others) depending upon the context of the situation, the people involved and the task at hand. Leaders need to build capabilities in all areas of leadership.

Transformational leadership is more popular because it focuses on transforming the school to achieve objectives of education to suit the present age of information and technology. It fosters relationship between present and future needs of education. The learners are to be exposed to their individual needs and needs of the society in the interest of global demands.

In my opinion there should not be one or two leaderships styles. In difirrenent situations and with different people to manage, all leadership styles can be used by the same principal in order to be effective.

The role of a school leader should be to serve and empower teachers, fostering a culture that will respect its member’s decisions within the frame of exchanging ideas .

As Deal and Peterson (1994), argue that: ‘High performing organizations have both order and meaning, structure and value’. Thus, school leaders must have both the technical skills of an engineer and the creative imagination of an artist. In addition, the creation of supportive conditions should be promoted by servant-leadership, with the leader to be the steward.

Deal, T.E., Peterson, K. (1994).The Leadership Paradox: Balancing logic and artistry in schools. San Francisco, CA: Jossey-Bass.

In my "humble" opinion, the best is the authoritative style which is inclusive of reliability, honesty, trust, and confidence. This style of leadership is expected to, e.g. listen to every one under his/her command, encourage independence & team work in a delicate balance, express warmth & modesty towards all the staff members, administer fair & consistent discipline equally, and fight hypocrisy.

I haven't seen a single leadership style followed by any school leader, specially in a successful school

The reason being that there is no successful school leadership model that can be applied in all schools, around the world.

My findings are that all successful school leaders are contextual leaders; they pick and choose their style from several available models based upon their own school contexts. School contexts are unique and leadership style should match the contexts.

I worked as school teacher in Jordan between 1975 & 1978 under 2 principals "one served for 1 year & the other for more than the following 2 years I was at that school". Within the 3 years, the over-all surrounding situation did not change. However, there was a huge difference between the 2 principals in terms of leadership. When a teacher mate was transferred to that school, he went straight to the 1st principal's office to find 2 men sitting there "the principal & the school's janitor" so he asked: Who is the headmaster of the school ? My mate told me ,later on, that he asked the question deliberately! Had he transferred in the era of the 2nd principal, he would not have asked this question because the second was a true authoritative charismatic leader. 

Despite many leadership styles, finding most of them are surrounding within these 4 common entities (see link below for the diagram).  Think the best way to lead is to consider these 4 entities / factors i.e. the leader own attributes, followers' attributes, types of goals and the environment they are in.

https://www.researchgate.net/post/What_is_the_best_definition_of_a_leader

The most popular leadership style is the visonary leader just like the silent leader it takes patience and a behavior that is not drwan upon self interests but to harness and direct with great responsibility for change. The practical leadership is runner-up, it requires one to embrace complexity, invest wisely and to inspire others.